It took the U.S. just a dozen minutes to throw away a decade of dominance against Mexico, each of three goals stripping away another layer of invulnerability vs. its rival. It took this young team just that long to lose its poise and then its pride, crumbling in a 5-0 Gold Cup final loss — its worst defeat in nearly a quarter-century.

The United States had not lost to Mexico outside of daunting Azteca Stadium in 11 straight games since March 13, 1999, and it hadn’t been drilled by anybody this badly since a 5-0 loss to England back in June 1985. But yesterday, this raw U.S. B-team imploded on the big stage.

“I’m [ticked]. If you’re an American and you’re not [ticked], then there’s something wrong with you. We’re just going to channel this anger, use it on Aug. 12,” said forward Brian Ching, the only U.S. starter with a chance to line up for the more important World Cup qualifying rematch in Mexico City.

“Standing on the field watching them accept the trophy, that’s going to be in my mind for a long time. I’m not going to need more motivation than that.”

The vast majority of a sellout crowd of 79,156, the biggest ever for a soccer game at Giants Stadium, booed the U.S., turning the Meadowlands into Mexico City for a day. And while El Tri wore green, it was the inexperienced U.S. that looked green, unraveling late.

“The second half for us . . . that’s not what we’re about,” said coach Bob Bradley. “When you have to stand there and see the other team get medals and hold up the trophy, that’s a feeling you don’t like. You hope those things help you grow.”

When defenseman Jay Heaps got called for wrestling Man of the Match Giovani Dos Santos down in the box, Gerardo Torrado buried a 56th-minute penalty kick for Mexico’s first goal.

The U.S. capitulated, getting befuddled and beaten on offside traps the rest of the day.

“After that, they played with a lot more energy and we didn’t deal with it,” said goalkeeper Troy Perkins. “You could just see our body language go down. We couldn’t pick ourselves up. We’re men. We’ve got to be able to move on, push and fight back, and we just weren’t there.”

Carlos Vela, who changed the game when he replaced ineffective Alberto Medina at halftime, beat defenseman Clarence Goodson down the left wing, and passed to Miguel Sabah. Perkins saved his shot, but the ball bounced to Dos Santos for a tap-in.

Dos Santos, great after moving back into midfield, hit Vela on a counter, and his acute-angle chip beat Perkins in the 65th minute. Vela’s pass split Goodson and Chad Marshall to set up Jose Antonio Castro; and after Heaps’ second yellow left the U.S. with 10 men, Guillermo Franco provided a 90th-minute coup de grace.

“We lost our composure and they punished us,” said Ching of a Mexican team that used half its starters. “If they think that game’s [on Aug. 12] going to be anything like this they’ve got another thing coming.”

It’s the latest log on the fire of a rivalry that has seen U.S. players pelted with bags of urine in Azteca, and ex-Mexico fullback Edgar Castillo in the process of switching sides. Yesterday will give El Tri, whose woes were more mental than physical, a big boost.

Of playing a U.S. “C” team, Dos Santos said: “We didn’t have all of our players. It doesn’t matter. We were the better team.

“This injects motivation, security and confidence in us. We’re going to enjoy this and think about Aug. 12.”

So will the U.S. — it will just be a different U.S. And it can only hope a better one.